1. Field of the Invention
This invention relates to a color fluorescent luminous tube of the type of including a plurality of luminous cells, cathode filaments stretched opposite to the luminous cells, and control grids and shield grids arranged between the luminous cells and the cathode filaments, and more particularly to such a color fluorescent luminous tube which is adapted to effectively remove impurities generated in the luminous tube.
2. Description of the Prior Art
A picture cell luminous tube for a large-sized display or the like has been conventionally proposed which is typically constructed in such a manner as shown in FIG. 1. More specifically, the conventional picture cell luminous tube includes a plurality of luminous cells separated from one another by diffusion plates 2. The luminous cells 1 have phosphors of, for example, red, green and blue luminous colors deposited thereon, respectively. The picture cell luminous tube also includes a cathode filament 3 stretched above each of the luminous cells 1 to be opposite thereto and a control grid 4 and a shield grid 5 arranged between the luminous cell 1 and the cathode filament 3. In the picture cell luminous tube constructed in such a manner, the control grid 4 controls the passage of electrons emitted from the cathode 3 to allow only electrons for a region of the luminous cell 1 which is to emit light to selectively pass through the control grid 4. Then, the electrons pass through the shield grid 5 and then is subjected to the diffusion action of the diffusion plate 2 so that the electrons may uniformly impinge upon the overall surface of the luminous cell 1 to cause it to emit light.
Recently, a color fluorescent luminous tube constructed as described above has been extensively used in a variety of fields. Particularly, it is expected to be widely used as a picture cell for such a large-sized display device as represented by a super color television.
In order that a color fluorescent luminous tube can be effectively used as a picture cell for a super color television or the like, it is essential to keep an anode at high voltage to cause electrons to impinge on a luminous cell adjacent to the anode with a high speed. Otherwise, it fails to increase a luminous area and exhibit high luminance. However, in a conventional color fluorescent luminous tube as described above, when high speed electron beam impinges upon a luminous cell, phosphor deposited on the luminous cell such as, for example, Y.sub.2 O.sub.2 S:Eu of red luminous color, ZnS:CuAl of green luminous color, ZnS:Ag of blue luminous color or the like is decomposed due to the irradiation of the high speed electron beam to directly produce sulfide gas such as S, SO and/or SO.sub.2 or cause sulfide gas trapped in the phosphor to ooze out. Alternatively, the produced gas chemically bonds to oxygen which is produced due to the decomposition of residual H.sub.2 O by the high speed electron beam. Further, the irradiation of the high speed electron beam causes H.sub.2, C, Cl.sub.2 adhered to the wall of the luminous tube to be rendered free due to impingement of the beam thereon, resulting in sulfide gas such as S, SO, SO.sub.2 or the like being generated from the surface of the luminous cell. The produced sulfide gas chemically bonds to a material coated on a cathode filament such as, for example, (Ba, Sr, CaO)Ba or adheres to the cathode filament, which results in deterioration of the electron emitting capacity of the cathode filament, to thereby cause a phenomenon called cathode poisoning and substantially reduce the life of the fluorescent luminous tube.